ALEXEI KOJEVNIKOV* Freedom, collectivism, and quasiparticles: Social metaphors in quantum physics Fermions are individualists, while bosons are collectivists.1 1. FREEDOM AS PROBLEM WHAT KIND OF freedom do scientists have inmind when they say that an elec tron or another particle "is free"? The most common model of a system of free particles is an ideal gas, inwhich atoms are rare and move unfettered, interacting onlywhen theydirectly collide. Yet some physicists, such as Yakov Frenkel, whose specialty was the quantum theoryof matter and whose political views were social ist, observed that in this system, only atoms are free, but electrons are not. They on are, the contrary, enslaved by free atoms. If, however, atoms are packed to gether closely into a solid body, they lose most of theirfreedom and become con fined to specific loci of a crystal, but in this very same process, electrons gain in freedom as theybecome liberated from individual atoms. on *Center for History of Physics, American Institute of Physics, College Park, MD 20740; leave from the Institute for History of Science and Technology, Russian Academy of Sci ences; e-mail: [email protected]. I am grateful to Stephen Brush, Cathryn Carson, Olivier Darrigol, Paul Forman, Joel Genuth, J.L. Heilbron, John Krige, Sylvan Schweber, Jessica Wang, and Spencer Weart for comments. The following abbreviations are used: AHQP, Archive for the History of Quantum Phys ics (Officefor History of Science andTechnology, University of California, Berkeley); AP, Annalen der Physik', BSSP, The beginnings of solid state physics. A symposium organized by SirNevill Mott, F.R.S. Held 30Apr-2 May 1979 (London 1980); FPW(Frenkelpopular writings), Ya.I. Frenkel. Na zare novoifiziki. Sbornik izbrannykh nauchno-populyarnykh rabot (Leningrad: Nauka, 1970); FSW (Frenkel selected works), Ya.I. Frenkel, Sobranie izbrannykh trudov, vols. 1-3 (Moscow-Leningrad, 1958-59); OCM, Lillian Hoddeson, Ernest Braun, Jiirgen Teichmann, and Spencer Weart, eds., Out of the crystal maze. Chapters from thehistory of solid statephysics (Oxford, 1992); PR, Physical review;PZSU, Physikalische Zeitschrift der Sowjetunion; TCW(Tamm collected works), I.E. Tamm. Sobranie nauchnykh trudov (2 vols., Moscow, 1975); YIF, Victor Ya. Frenkel. Yakov Rich Frenkel. His work, life and letters. (Basel, 1996); ZhETF, Zhurnal eksperimentaVnoi i teoreticheskoi fiziki; ZP, Zeitschriftfur Physik. 1. M.I. Kaganov, I.M. Lifshits, Kvazichastitsy, 2nd. ed. (Moscow, 1989), 14. HSPS, 29:2(1999) 296 KOJEVNIKOV Liberated intowhat state?The answer is not simple. In a metal, electrons trans port electric current and, therefore,are apparently free enough tomove through the solid body. On the other hand, they are still subject to very strong forces from the atoms of the crystal lattice as well as from other electrons. Some physicists described thiscomplext situationwith thehelp of electrons belonging to theirproper atoms and only occasionally switching theirallegiances, while others envisioned electrons as almost free, an ideal gas of their own. Frenkel and some similarly minded colleagues felt that neither of these alternative descriptions was close to electrons' real state of freedom,which he referred towith a special word: "collec tivist."The idea came from leftistpolitical language and social theory. Disagreements over the large issue of freedom played a particularly important role during the early formative stages of the quantum physics of the solid, liquid, and plasma states of matter?or condensed matter in the current usage?from the 1920s through the 1950s. At stakewas not only the language proper, but themath ematical models and conceptual foundations of an emerging scientific discipline. A variety of specific approaches and theories that existed and competed during thatperiod rested on theirauthors' conflicting intuitions regarding the freedom of particles. In theirattempts to conceptualize these intuitions in physical and math ematical terms,physicists often used social metaphors, implicitly as well as ex plicitly, consciously as well as unconsciously. These metaphors reflected their varying interpretations?liberal and collectivism among others?of the general concept of freedom, theirpolitical philosophies, and also theirpersonal and often incompatible existential experiences of social life in different countries and re gimes. The present paper studies one line in this debate: the collectivist approach in the early history of condensed matter physics and its corresponding collectivist metaphors.2 Iwill follow attemptsby socialist-minded physicists to develop meth ods for the description of the collective behavior of particles, which led them to several new physical models, laterunited under thegeneral termquasiparticles. As basic objects in virtually all fields of current research on the properties ofmatter, including some half-dozen Nobel prize-winning works, quasiparticles are familiar to any practicing physicist and, since the 1950s, belong among themost funda mental concepts of physics. Little is known, however, about theirhistorical kin shipwith collectivism. The relationship dates back to the firsthalf of the century when socialist ideas thrived and when the foundations of thephysics of condensed matter were laid. Physicists in the field today much more commonly work for business than for leftistpolitical causes, but they continue speaking collectivist language. Its success is partly related to the fact that its relationship with the by 2. This approach has not been studied so far in the existing historical literature. For more information on the history of other main approaches, see, in particular, OCM. This paper may be considered an additional chapter for that landmark study. QUANTUM PHYSICS 297 now largely discredited political movement has become invisible, just likemany other legacies of socialism in contemporary life. "Collectivism," like "freedom," was used and abused somuch in political pro paganda that it seems necessary to startwith clarifications of itsmeanings. As if in order to remind us thatwords sometimes have tricky trajectories, "collectivism" as a political termoriginated with opponents ofMarxism. It referred to the theory that themeans of production should be owned neither by private individuals nor by the state, but by free associations of laborers. The conflict between Mikhail Bakunin and other proponents of thisview with Karl Marx and his followers led to the splitof theFirst International in 1872. The new political movement thatformed thereafteraccepted collectivism as its program and anarchism as its name. The anarchists were the Marxists' main rivals within the international workers' move ment, having strongholds inFrance, Switzerland, Spain, and Italy.They continued to be a powerful forcewithin theEuropean leftuntil their last importantorganiza tionswere exterminated in the 1930s, especially during the Spanish Civil War.3 Much earlier, however, by 1900 at least, anarchists had lost theirmonopoly over the term"collectivism." Although theyand some others continued to use it in defense of workers' freedom against both private and state property, theword was also appropriated by virtually all socialist factions. Itsmeaning changed, too, as it ever more as a began to be used often vague synonym for anti-capitalist values, while its critique of etatisme weakened. Socialists accepted collectivism as an al ternative to the liberal individualist concept of freedom, noting that the latteroften went hand inhand with exploitation and slavery.4 Collectivism, for them,was the true strategyof liberation for the oppressed and their only way to succeed in the struggle for freedom. The nextmajor change ofmeaning occurred owing to collectivization, a violent reformof Soviet agriculture around 1930. Legally, the Soviet kolkhoz was a coop a erative of peasants, not state enterprise, which was a large concession from the point of view of hard-core Marxists. The kolkhoz thus had some formal resem blance with the original anarchist program, although it in factwas anything but a free association. The results of collectivization were notoriously disastrous. Among other,more important things, they also damaged the reputation of collectivism, showing thatwhat had been conceived as a liberation concept could also become a method of enslavement. In this,as in a number of other importanthistorical cases, the pursuit of a new type of freedom in the political realm turned into the emer gence of a new type of dictatorship. A similar pursuit in the realm of physical models produced a different outcome, leading to the discovery of new kinds of natural objects. 3. On anarchist collectivism see Max Nettlau, A short history of anarchism (London, 1996), chapt. 8; George Woodcock, Anarchism: A history of libertarian ideas and movements (Cleve land, 1962). 4. On this and other antinomies of freedom see, for example, Zygmunt Bauman, Freedom (Minneapolis, 1988). 298 KOJEVNIKOV 2. QUASIPARTICLES New objects started to appear in solid state physics around 1930, when all of themeanings of collectivism discussed above were still inwide circulation. Their current name, quasiparticles, was introduced afterWorld War II. In their early decades, these new objects were most commonly referred to as "collectivized" particles or as "collective excitations." A basic idea indicative of theirname may be illustratedby two simple examples. Consider a stringof connected atoms, one of which is in an excited state. Since it interactswith neighboring atoms, it can